In general, waste energy recovery systems for use with engines need to operate over a wide range of heat input, which varies depending upon the engine load, while maintaining acceptable performance under conditions of high fuel consumption. Various systems for adjusting system performance over a heat input range are known, such as those described in U.S. Pat. No. 6,986,251, for example.
One function of engine cooling systems is to reduce the temperature of gases provided to the intake manifold of the engine in certain engine designs. Some gasoline and diesel engine systems employ exhaust gas recirculation techniques which re-route a portion of the exhaust gas from the engine, which ordinarily would be expelled by the vehicle exhaust system, back to the engine's intake manifold. This recirculated exhaust gas is mixed with incoming fresh air, and lowers the peak combustion temperature, thereby limiting the generation of harmful emissions, such as nitrogen oxides. However, the high temperature exhaust gas recirculated to the engine increases the temperature of the incoming mix, and therefore increases the demands on the engine's cooling system. This increased demand for heat rejection may require a larger radiator. In vehicular engine systems where space is limited, increasing the size of the radiator is a difficult engineering challenge.